The mass of the books is 1.8 kg = 1800 g more than the empty bag.<br><br>
[[model:questions/solutions/q4642.png]]<br><br>
&bull; Let the empty bag = 1 unit<br>
&bull; Books = 1 unit + 1800 g<br>
&bull; Total (bag + books) = 1 unit + 1 unit + 1800 = 2 units + 1800 = 3450 g<br>
&bull; 2 units = 3450 − 1800 = 1650 g<br>
&bull; 1 unit = 1650 ÷ 2 = 825 g (empty bag)<br>
&bull; Mass of books = 825 + 1800 = 2625 g<br><br>
The mass of the books is 2625 g.<br>
Check: 825 + 2625 = 3450 g total. ✓